Micromechanical Thermal Assays of Ca2+-Regulated Thin-Filament Function and Modulation by Hypertrophic Cardiomyopathy Mutants of Human Cardiac Troponin

Abstract EN

Microfabricated thermoelectric controllers can be employed to investigate mechanisms underlying myosin-driven sliding of Ca2+-regulated actin and disease-associated mutations in myofilament proteins.

Specifically, we examined actin filament sliding—with or without human cardiac troponin (Tn) and α-tropomyosin (Tm)—propelled by rabbit skeletal heavy meromyosin, when temperature was varied continuously over a wide range (∼20–63C°).

At the upper end of this temperature range, reversible dysregulation of thin filaments occurred at pCa 9 and 5; actomyosin function was unaffected.

Tn-Tm enhanced sliding speed at pCa 5 and increased a transition temperature (Tt) between a high activation energy (Ea) but low temperature regime and a low Ea but high temperature regime.

This was modulated by factors that alter cross-bridge number and kinetics.

Three familial hypertrophic cardiomyopathy (FHC) mutations, cTnI R145G, cTnI K206Q, and cTnT R278C, cause dysregulation at temperatures ∼5–8C° lower; the latter two increased speed at pCa 5 at all temperatures.